1. Field of the Invention
The present invention relates to a recording material such as a recording paper. More particularly, it relates to a recording material on which the coloring property of an ink comprising a water soluble dye is excellent and a printed image has high resolution and water and light resistance.
2. Description of the Related Art
In an ink jet printing method, droplets of ink are formed by various mechanisms and injected from nozzles onto a surface of a recording material such as a paper sheet to print an image thereon. Since the ink jet printing is very quiet and generates images very quickly and can record images with various colors, it is increasingly used in a printing field.
As the recording material for ink jet printing, conventional paper has been used generally. However, with improvement of the ink jet printing machine such as an increase in recording speed and/or multicoloring and with the enlargement of application fields, the recording material is now required to have improved properties. That is, for recording a colored image having substantially the same resolution and quality as a color photograph, the recording material should satisfy the following requirements:
1. The recording material absorbs the ink quickly.
2. When two or more dots overlap with each other, the subsequently injected ink does not migrate over the already printed dot(s).
3. The ink forms a substantially round dot and the dot periphery is smooth.
4. The diameter of an ink dot is not unnecessarily enlarged.
5. The ink concentration in the dot is high and the dot periphery is not blurred.
6. The ink exhibits a good coloring property on the recording material. In addition, the ink is required to exhibit good resistence to water and light.
However, no recording material that satisfies all of the above requirements has been developed.
To increase ink absorption of the recording material, various attempts have been made, for example, impregnation of a water-soluble polymer in a paper sheet to which urea-formaldehyde resin powder is internally added (Japanese Patent Kokai Publication No. 49113/1978), formation of an ink absorbing coating layer on a paper sheet (Japanese Patent Kokai Publication No. 5830/1980) and use of non-glued silica powder as a pigment in the coating layer (Japanese Patent Kokai Publication No. 51583/1980). Although ink absorption is somewhat increased by these methods, the printed image lacks water resistance.
To solve this problem, it has been proposed to render the printed ink water resistant by adding to the recording material a cationic polymer such as polyethyleneimine, polyvinylpyridinium halide (Japanese Patent Kokai Publication No. 84992/1981) and dimethyldiallylammonium chloride (Japanese Patent Kokai Publication No. 20696/1984). However, the improvement of water resistance of the printed ink is still unsatisfactory and the light resistance of the ink decreases.